Method of making a pneumatic radial tire with carcass overlap joint having at least one circumferential cut

ABSTRACT

A pneumatic radial tire comprises a radial carcass ply wound around the axis of the tire over one turn so that the terminal edge of the winding of the carcass ply overlaps with the starting edge thereof to define an overlap-joint part, the overlap-joint part provided in one of the starting edge and terminal edge with at least one cut by which carcass cords existing therein are cut, and a method of making the same comprises the steps of cutting the starting edge prior to winding a carcass strip or cutting the terminal edge prior to the end of winding a carcass strip.

This application is a divisional of application Ser. No. 08/545,921,filed on Oct. 20, 1995, now U.S. Pat. No. 5,658,405, the entire contentsof which are hereby incorporated by reference.

The present invention relates to a pneumatic radial tire and a method ofmaking the same, in which occurrence of the dent resulting from aoverlap-jointing of a carcass ply is decreased and the tire qualitiessuch as uniformity, appearance, durability and the like can be improved.

BACKGROUND OF THE INVENTION

It is well known that the radial tires are excellent in high speedrunning performance because a rigid belt is disposed outside the carcasscrown portion such that the tread rigidity is increased. Further, thebelt decreases a load on the carcass, which makes it possible to reducethe number of the carcass plies.

When making a conventional radial tire, as shown in FIG. 7, a carcassply strip (a) is wound in a cylindrical shape on a former F, and theterminal edge 2 of the winding is overlapped with the starting edge 1thereof to connect or joint thereto. In the finished tire, as shown inFIG. 8, this overlap-joint part (A) extends in the radial directionalong the carcass cords. As a result, when the tire is inflated, a socalled "joint-dent", a phenomenon that the outer surface of the sidewallportion dents along the overlap-joint part (A), is caused. Inparticular, if the joint-dent exceeds 0.4 mm, the tire appearance,durability, uniformity and the like are greatly deteriorated. Further,the dent is remarkable when the number of the carcass plies is small,especially when the carcass consists of a single ply, thereby a tireweight reduction can be hindered.

If the width-of the overlap-joint part (A) is decreased to reduce thejoint-dent, the carcass ply opens at the overlap-joint part (A) duringshaping of the carcass, and the prevention of the opening necessitatesan overlapping of at least two to four carcass cords.

SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide apneumatic radial tire in which the joint-dent is reduced.

Another object of the present invention is to provide a method of makingsuch a pneumatic radial tire.

According to one aspect of the present invention, a pneumatic radialtire comprises

at least one carcass ply of cords extending between bead portionsthrough a tread portion and sidewall portions and turned up around beadcores,

the carcass ply being wound around the axis of the tire over one turn sothat the terminal edge of the winding of the carcass ply overlaps withthe starting edge thereof to define an overlap-joint part, wherein

the overlap-joint part is provided in one of the starting edge andterminal edge with at least one cut along the circumferential directionof the tire by which carcass cords existing therein are cut.

According to one aspect of the present invention, a method of making thepneumatic radial tire comprises the steps of

winding a carcass strip on a former around the axis of the former overone turn to form the carcass ply,

overlapping the terminal edge with the starting edge of the winding ofthe carcass strip to form the overlap-joint part, and

cutting one of the starting edge and terminal edge in the overlap-jointpart along the circumferential direction of the tire at at least oneposition to form at least one cut by which carcass cords existingtherein are cut.

In the above-mentioned conventional overlap-joint part (A), the numberof the carcass cords which extend continuously from bead to beadincreases in comparison with the remaining part, and as a result, thecord tension becomes relatively small and the cord elongation becomesrelatively decreased. Accordingly, a dent is formed along theoverlap-joint part.

However, in the overlap-joint part of the present invention, cordsexisting therein are cut and lose a function as a tension member.Therefore, the cord tension can be evened, and the joint-dent can beeffectively prevented.

Further, it becomes possible to provide a sufficient overlapping widthwithout causing a dent, and accordingly, the above-mentioned opening ofthe overlap-joint part during shaping of the carcass can be prevented.As a result, the tire manufacturing efficiency and working efficiencycan be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be explained according todrawings.

FIG. 1 is a schematic perspective view showing a pneumatic radial tireaccording to the present invention.

FIG. 2 is a schematic perspective view showing the carcass thereof.

FIG. 3 is a schematic cross sectional view for explaining the steps ofwinding the carcass strip and forming the overlap-joint part.

FIG. 4 is a schematic perspective view for explaining the step offorming the cut.

FIG. 5 is a diagram for explaining another example of the cuts.

FIG. 6 is a diagram showing the effect of the present invention.

FIG. 7 is a schematic perspective view showing the conventional carcassstrip wound on a former.

FIG. 8 is a schematic perspective view showing the conventional carcassin the finished tire.

DETAILED DESCRIPTION OF THE DRAWINGS

In the drawings, a pneumatic radial tire 3 according to the presentinvention is a tubeless radial tire.

The tire 1 comprises a tread portion 2, a sidewall portion 3 extendingradially inwardly from each edge of the tread portion, a bead portion 4disposed at the radially inner end of each sidewall portion 3, a beadcore 5 disposed in each bead portion 4, a carcass 6 extending betweenthe bead portions 4, an inner liner 7 disposed on the inside of thecarcass 6 and facing the tire cavity H, and a stiff belt layer 9disposed outside the carcass 6 in the tread portion 2.

The inner liner 7 is an air-tight rubber layer made of, for example,butyl rubber and protects the inner surface of the carcass 6.

The belt layer 9 in this embodiment comprises a radially inner belt ply9A and a radially outer belt ply 9B, each ply made of cords laid at, forexample, an angle of not more than 30 degrees with respect to the tireequator C, so that the cords in the belt ply 9A are laid crosswise tothe cords in the belt ply 9B, to reinforce the substantially whole widthof the tread portion 2 and to increase the tire rigidity.

For the belt cords, various cords such as organic fiber cords, e.g.nylon, rayon, polyester and aromatic polyamide, inorganic fiber cords,e.g. steel cords and the like can be used.

The carcass 6 consists of at least one radial ply 6A, in thisembodiment, as shown in FIG. 2, consists of a single carcass ply 6A. Thecarcass ply 6A is made of carcass cords 8 arranged at an angle ofsubstantially 90 degrees, about 80 to 90 degrees, with respect to thetire equator C. The carcass ply 6A extends between the bead portions 4through the tread portion 2 and sidewall portions 3 and turned up aroundthe bead cores 5 from the axially inside to the outside of the tire toform a pair of turned up portions 6A2 and a toroidal main portion 6A1therebetween.

For the carcass cords 8, various cords such as organic fiber cords, e.g.nylon, rayon, polyester and aromatic polyamide, inorganic fiber cords,e.g. steel and the like can be used.

Between the main portion 6A1 and turned up portions 6A2, each beadportion 4 is provided with a bead apex rubber 10 extending radiallyoutwardly taperingly from the radially outer surface of the bead core 5so as to reinforce the bead portion and sidewall lower portion and toincrease the tire rigidity.

The carcass ply 6A is wound circumferentially of the tire over one turnso that the terminal edge E2 of the winding or windings overlaps withthe starting edge E1, defining an overlapping part 11.

According to the present invention, carcass cords 8 in the carcass mainportion 6A1 in the overlap-joint part 11 are cut so that at least onecut 12 is provided in one of the starting edge El and the terminal edgeE2.

In FIG. 2, only the radially outward terminal edge E2 is provided on thetire equator C with only one cut 12 extending in the circumferentialdirection of the tire.

Accordingly, the overlap-joint part 11 decreases in the pull resistanceand is allowed to elongate or expand by applying the tire innerpressure. As a result, the joint-dent can be reduced.

Besides the tread portion 2, such a cut 12 can be provided in a tireshoulder portion 14 and/or sidewall portion 3.

In FIG. 5, five cuts 12 are provided, one cut in the tread center, twocuts in the shoulder portions 14 and two cuts in the sidewall portions3. If a plurality of cuts 12 are provided, the cuts are preferablyarranged symmetrically about the tire equatorial plane C.

The width W of the overlap-joint part 11 is preferably set to correspondto 3 to 8 carcass cords, that is, 3 to 8 times the cord diameter+thecord space. If the width W is less than 3 cords, the overlap-joint part11 is liable to open at the time of shaping the carcass. If more than 8cords, it is difficult to keep the dent under 0.4 mm.

When the carcass 6 consists of a plurality of plies 6A and as a result aplurality of overlapping parts 11 are formed in differentcircumferential positions, each of the overlapping parts 11 must beprovided with at least one cut 12 as explained above. However, theeffect of controlling the occurrence of joint-dent is most remarkablewhen the carcass 6 consists of a single ply 6A.

According to the present invention, a method of making the tire 1comprises the steps of

winding a carcass strip 15 on the former F around the axis thereof overone turn to form the carcass ply 6A as shown in FIG. 3,

overlapping the terminal edge E2 with the starting edge E1 of thewinding of the carcass strip 15 to form the overlap-joint part 11 asshown in FIG. 4, and

cutting one of the starting edge El and the terminal edge E2 of theoverlap-joint part 11 along the tire circumferential direction at atleast one position to form at least one cut 12 by which carcass cords 8existing therein are cut as shown in FIGS. 4 and 5.

Example tires having the structure shown in FIG. 1 and a conventionaltire having the carcass structure shown in FIG. 8 were made and measuredfor the joint-dent. The results are shown in FIG. 6.

As shown in FIG. 6, it was confirmed that the dent of the Example tireswas decreased to about one half of that of the prior art tire, and thetire uniformity, appearance, durability and the like were improved.

Further, it was confirmed that the number of the carcass cords existingin an overlapping part could be increased up to eight while maintainingthe joint-dent in the range of less than 0.4 mm, and the tiremanufacturing efficiency and working efficiency could be improved. Theinvention being thus described, it will be obvious that the same may bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art intended tobe included within the scope of the following claims.

I claim:
 1. In a method of making a pneumatic radial tire, theimprovement comprising the steps of,winding a carcass strip around theaxis of a former over one turn to form a carcass ply, overlapping theterminal edge with the starting edge of the winding of said carcassstrip to form an overlap part, and cutting one of said starting edge andterminal edge in said overlap part at one position to form only one cutextending in a circumferential direction of the tire by which carcasscords existing therein are cut.
 2. The method of making a pneumaticradial tire according to claim 1, whereinsaid one of said starting edgeand terminal edge is said starting edge and the step of cutting thestarting edge is prior to the step of winding the carcass strip.
 3. Themethod of making a pneumatic radial tire according to claim 1,whereinsaid one of said starting edge and terminal edge is said terminaledge and the step of cutting the terminal edge is prior to the end ofthe step of winding the carcass strip.